1. Field of the Invention
The present invention relates to a system or a method for measuring flow of fluid or gas, which system comprises a flow duct, which flow duct comprises at least two transducers, which transducers generate at least one beam of ultrasound in the flow duct, which Transmitter/receiver circuits are connecting through a transmitter/receiver switch, which switch in a first position connect first Transmitter/receiver circuit to a transmitter circuit and second transducers are connected to a receiver circuit, which receiver circuit comprises at least a band pass filter, which band pass filter is further connected to a microcontroller, which microcontroller comprises an analogue to digital converter, which digital converter converts the analogue signal into digital data samples representing at least transit times and time difference, which microcontroller stores the data samples in a memory.
2. Description of Related Art
International Patent Application Publication WO 2010/122117 discloses a ventilation system, wherein a fan draws air from an exterior of a building or similar closed construction for circulation into an interior of the building, and produces supply airflow through a ventilator unit, which is able to cool and heat air. Moreover, the ventilator unit may be equipped with a humidifying/dehumidifying device. A controller controls the position of a valve or indirectly the speed of the fan, thereby adjusting the supply airflow in response to an input received from an ultrasound device placed in the supply air duct, wherein the ultrasound device measures the air flow and temperature.